Along with advance in research on genetic information analysis of various living organisms, more information about a number of genes including human genes and their base sequences as well as the proteins coded by the gene sequences and the sugar chains produced there proteins secondarily is becoming available rapidly. The functions of the macromolecules such as gene, protein, and sugar chain with distinct sequence can be studied by various methods. For example as for nucleic acids, mainly, the relationship between various genes and their biological functions can be studied for example by using the complementarity of a nucleic acid and another nucleic acid such as Northern hybridization or Southern hybridization. As for proteins, it is possible to study the function and expression of proteins such by methods of using protein/protein interaction such as Western hybridization.
In recent years, a new assay method or methodology called DNA microarray method (DNA chip method) was developed and attracting attention recently as a method of analyzing expression of multiple genes at the same time. All these methods are the same in principle as conventional methods, because they are methods of detecting and quantifying nucleic acids based on hybridization reaction between nucleic acids, and applicable to detection and quantification of proteins and sugar chains based on the interaction between protein/protein, sugar chain/sugar chain, or sugar chain/protein. These methods are characteristic in that a piece of flat glass substrate called microarray or chip carrying multiple DNA fragments, proteins, or sugar chains that are immobilized densely is used. Typical examples of the use of the microarray method include a method of hybridizing a gene expressed in analyte cell with a sample labeled, for example, a fluorochrome on a flat substrate, allowing mutually complementary nucleic acids (DNA or RNA) to bind to each other, and detecting the binding sites rapidly in a high-resolution analyzer; and a method of detecting the response such as the change in electric current due to an electrochemical reaction. In this manner, it is possible to estimate the amounts of the genes present in sample.
For example, Japanese Patent Application National Publication (Laid-Open) No. 10-503841 (Claims) discloses a method of coating poly-L-lysine, aminosilane, or the like on a flat substrate such as slide glass and immobilizing nucleic acids by using a spotting device called spotter, as the method for immobilizing a nucleic acid on substrate.
Alternatively, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-108683 discloses a method of using oligo-DNAs (oligo-DNA is a DNA having a base number of 10 to 100) as nucleic acid probes used on DNA chip (nucleic acids immobilized on substrate) instead of the conventional method of using cDNAs and the fragments thereof having base lengths of hundreds of thousands, for reduction of error during detection and convenience of synthesis in synthesizer. In the method, the oligo-DNAs are bound to the glass plate covalently.
In addition to glass, there are some proposals on resin substrates, as the material for used as the substrate for DNA chip. For example, JP-A No. 2001-337089 (Paragraph 17) describes a polymethyl methacrylate polymer. However, JP-A No. 2001-337089 discloses no specific method of immobilizing DNA. In addition, JP-A No. 2003-130874 (Paragraph 12) also has a similar description but discloses no specific method of immobilizing DNA. JP-A No. 2002-71693 (Paragraph 7) discloses a method of modifying a nitrile group-containing fiber such as acryl fiber into a carboxyl group-containing fiber by alkali treatment and immobilizing DNAs or the like by bonding the carboxyl groups. However, the alkali fiber, which contains polyacrylonitrile as the main component, has a problem that it has a high autofluorescence as it is and is not suitable as a substrate. Further, JP-A No. 2002-71693 (Paragraph 7) discloses a method of modifying polymethacrylate by copolymerization with acrylic acid or methacrylic acid into a carboxyl group-containing fiber and allowing the carboxyl groups to bind to DNAs, but the method was disadvantageous in that the substrate (support) had a smaller amount of surface carboxyl groups leading to decrease in the amount of immobilized DNA and consequently insufficient intensity of the signal after hybridization.